Electromyographic study of the anterolateral abdominal wall muscles during ejaculation

Introduction. The anterolateral abdominal wall muscles (AAWMs) are composed of the external and internal oblique, transversus abdominis, and the rectus abdominis muscles. Aim. We investigated the hypothesis that the AAWMs contract reflexly during ejaculation. Methods Effect of coitus on AAWMs was tested in 16 healthy men (mean age 37.2 +/- 9.7 years). The intra-abdominal pressure was measured by a manometric catheter introduced into the rectum. The response of the AAWMs to erection and ejaculation was recorded before and after penile and AAWMs' anesthetization by a needle electrode inserted into each of the muscles. Main Outcome Measures. Electromyographic (EMG) activity of AAWMs and rectal pressure increased at ejaculation. Results. A few seconds before and during ejaculation, the rectal pressure and motor unit action potentials (EMG activity) of each of the AAWMs increased; this effect was abolished by anesthetization of the penis and AAWMs. Conclusion. Increased AAWMs' EMG denotes contraction of the said muscles. AAWMs' contraction at ejaculation, the resulting increase of the intra-abdominal pressure, and the presumably increased pelvic venous congestion seem to augment the penile venous congestion and rigidity. This effect is suggested to be mediated through a reflex which we call "ejaculation-abdominal wall reflex".